<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Document</title>
    </head>

    <body>
        <script>
            // 用户输入一个数，  计算 1 到这个数的累加和

            let num = prompt("请输入一个数：");
            let sum = 0;
            for (let i = 1; i <= num; i++) {
                sum += i;
            }
            document.write(`1-${num}的累加和是：${sum}`);
        </script>
    </body>
</html>
